1. Field of the Invention
This invention relates to screw grommets or nut devices of the type frequently referred to as insulated screw grommets or snap-in nuts. Devices having the characteristics embodied herein are primarily, but not exclusively, found in United States Art Class 85, Subclasses 80, 82, 83 and 84, under the general classification heading "Expanding Anchor" and Art Class 151 in the subclasses dealing with nuts having deformable and/or resilient retainers.
2. Description of the Prior Art
The use of screw grommets or snap-in nuts in the liners of foam filled refrigerators presently requires special sealing to prevent foam leakage through the hole. In the manufacturing techniques utilized today for making refrigerators, approximately 40% of the refrigerators made are insulated by a foamed in-situ material with the remainder being insulated with a fiberglass materal. It is anticipated that within the next few years all refrigerators will be insulated by a foamed material. The insulated grommets that are available on today's market will generally seal the aperture from the foam material to a certain degree but not completely. Usually a small amount of foam will leak out around the grommet with the foam being brushed off by an operator prior to insertion of a screw. This is acceptable on porcelain refrigerator liners because the foam does not attack the porcelain. However, more and more of the manufacturers are going in the direction of pre-painted or powder-painted cabinets in which the paint is subject to attack by the foam and, therefore, becomes an appearance problem. Additionally, it is necessary to seal the apertures in the liner from moisture which could move from the interior of the liner to the insulation compartment and would have a deleterious effect thereupon.
Previous efforts by other inventors are represented by the U.S. Pat. Nos. to Schuplin 3,342,098; Van Buren 3,703,120; and my own U.S. Pat. No. 3,830,134. Each of these devices is an insulated grommet or scew anchor which uses as its basis for operation the original teachings of the patent to Rapata U.S. Pat. No. 2,788,047, wherein a pair of leg members are disposed axially from the underside of the head to engage the walls of the aperture upon insertion of a screw in a central bore. In the case of the Schuplin patent and the Van Buren patent, they both utilize the teachings of Rapata with Schuplin adding a sack-like member to encircle the bore with the sack extending laterally outwardly beyond the margins of the legs, while the Van Buren device utilizes inwardly directed sack-like means for insulation purposes. My own prior patent, while completely serviceable for certain applications, utilizes a pair of spaced legs with an oval tubular member between the legs which is expanded to a cylindrical form upon insertion of a screw member therein. Related art can be found in the U.S. Pat. to Schulze No. 3,593,612, assigned to the common assignee of the present invention, as well as the patent to Rapata U.S. Pat. No. 3,803,973; a second patent to Schuplin U.S. Pat. No. 3,756,116; and a much older blind bore fastener issued to Scott U.S. Pat. No. 2,573,498. Each of these devices have shortcomings in that there is an opportunity in Schuplin '098, Van Buren '120 as well as my own '134 patent wherein the screw, if it is provided with a sharp point, can be cocked or angularly introduced into the bore and inadvertently puncture the sealing sack associated with one of these fasteners. With the fastener being a "blind" application, it is impossible to determine the presence of such interruptions in the sealing member associated with the fastener until after the damage is done. The patent to Schulze '612 represents a heavy rigid form of fastener which has a high insertion force into the aperture and lacks guarantees that the fastener is suitably seated with its head against the panel. Additionally, each of the devices mentioned generally have the disadvantage that in the manufacture there is a necessity for a parting line of the mold to be present on the undersurface of the head. The presence of this parting line, no matter how small, still does not permit total sealing of the head against the work panel around the aperture.